The present disclosure relates to a protective element interrupting an electric current in case of an unusual situation of a protection target device, and to a method for producing a protective element.
A related art chip-shaped protective element including a low-melting point metallic body (fuse element) disposed on a substrate has been known to prevent overcurrent associated with an unusual situation of a protection target device. In such a related art protective element, the fuse element blows when overcurrent is applied thereto in case of unusual situations. The blown fuse element is attracted to an electrode by good wettability with respect to an electrode surface on which the fuse element is placed. In the related art protective element, therefore, electric current is interrupted by blowing the fuse element.
Another related art chip-shaped protective element has also been known to prevent not only the overcurrent but also overvoltage. Herein, the related art chip-shaped protective element includes a heat generation resistor and a fuse element which are laminated on a substrate. In such a related art protective element, the electric current is applied to the heat generation resistor in case of the unusual situation, so that the fuse element is blown by heat generated by the heat generation resistor. The blown fuse element is attracted to an electrode by good wettability with respect to an electrode surface on which the fuse element is placed. In such a related art protective element, therefore, the electric current is interrupted by blowing the fuse element.
Each of such related art protective elements is generally mounted on a base circuit board of the protection target device by reflow soldering. Accordingly, the fuse element is made of a material having a high solid-phase point relative to a mounting temperature in order to prevent the fuse element from blowing when the related art protective element is mounted on the base circuit board. In addition, a method for mounting a related art protective element at a mounting temperature has been proposed (e.g., Patent Document 1). Herein, the mounting temperature is lower relative to the liquid-phase point of the fuse element while being higher relative to a solid-phase point of the fuse element.
Moreover, each of Patent Documents 2 and 3 discloses a related art protective element capable of interrupting the electric current using an elastic member in order to prevent the overcurrent or the overvoltage without disposing a fuse element.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-363630    Patent Document 2: Japanese Unexamined Patent Application Publication No. H9-306319    Patent Document 3: Japanese Unexamined Utility Model Application Publication No. S53-42145